The invention relates to a vehicle headlamp leveling device for automatically tilting the headlamps of a vehicle, and more particularly to a vehicle headlamp leveling device for vertically tilting the light axes of the headlamps based on pitch angles of the vehicle mainly when it is stationary.
A known automatic vehicle headlamp leveling device comprises a pitch angle detection sensor, a vehicle speed sensor and a controller for controlling the driving of actuators based on detected signals from the actuators which are mounted on a vehicle for adjusting the light axes of the headlamps (the reflectors) such that they stay in a given state relative to the surface of a road.
The known automatic vehicle headlamp leveling device is, however, constructed to level the headlamps of a vehicle in real time whether it is running or is at a stop. The device responds to a change in vehicle posture, which occurs when the vehicle accelerates or decelerates, or when luggage is loaded or unloaded or when occupants of the vehicle get in or out of the vehicle. Hence, the number of times the actuators are activated is high and consumption of power is also increased. Moreover, components of driving mechanism such as motors, gears and the like require tremendously high durability, which leads to increase in production costs.
An automatic headlamp leveling device was proposed in JP-A-2000-85458 that reduced the frequency at which the actuators are driven. The proposed device was constructed to control the actuators at certain intervals while the vehicle is at a stop, whereas when the vehicle is in motion, the driving of the actuators is controlled only once as long as the vehicle runs stably.
With the proposed device, when the vehicle turns, slaloms or runs on an irregular surface of a road at a constant speed, a vehicle height sensor, which is a pitch angle detection sensor, detects changes in pitch angle while the vehicle is running. However, when the vehicle is constantly running (i.e. running for a period of time during which the speed is equal to or more than a given value and the acceleration is equal to or less than a given value), the controller determines this condition as stable. Therefore, the headlamps can be inappropriately leveled based on pitch angle data detected during an unstable running condition such as turning, slaloming or running on irregular road surfaces.
When the vehicle turns left at a constant speed, the right-hand side suspension shortens or contracts because of a gravitational acceleration caused by the turn (hereinafter, referred to as turning G), and the vehicle height sensor attached to this suspension on the rear right wheel detects the sinking of the suspension as a tilt along the length of the vehicle as a change in pitch angle. On the other hand, when the vehicle turns right while running at a constant speed, the right-hand side suspension lengthens or expands because of a gravitational acceleration caused by the turn (hereinafter, referred to as turning G), and the vehicle height sensor attached to the suspension detects the expansion or floatation of the suspension as a tilt along the length of the vehicle as a change in pitch angle. A pitch angle data of turns is different from a pitch angle data detected during a stable running condition in which the vehicle runs on a flat surface of a road at a constant speed (which may be close to a pitch angle data detected while the vehicle is at a stop) and is inappropriate for use in leveling the headlamp.
However, the headlamp leveling device determines that a stable running condition is achieved when a speed of the vehicle is equal to or more than a given value and an acceleration of the vehicle is equal to or less than a given value for a predetermined period of time. Then the leveling (controlling) of the headlamps is carried out. If the leveling of the headlamps is carried out to lower the light axes, the visual distance in front of the vehicle is shortened. In terms of safety, this is not a preferable condition. Alternatively, if the leveling (controlling) of the headlamps is carried out to raise the light axes, on-coming vehicles may be subject to glare.
An object of the invention is to provide a headlamp leveling device that is inexpensive to produce, that provides a long service life by reducing the frequency at which actuators are activated, and that avoids inappropriate leveling of the headlamps while the vehicle is running.
A first implementation of a headlamp leveling device comprises headlamps adapted to be driven by actuators such that light axes thereof are tilted up and/or down relative to the body of a vehicle, control means for controlling the driving of the actuators, vehicle speed detection means for detecting the speed of the vehicle, pitch angle detection means provided on either of left and right suspensions of either of front and rear wheels for detecting a pitch angle of the vehicle, and a storage part for storing pitch angle data of the vehicle detected by the pitch angle detection means, the control means being adapted to control the driving of the actuators based on pitch angle data detected by the pitch angle detection means such that the light axes of the headlamps always stay in a predetermined tilted state relative to the surface of a road, wherein the control means determines whether the vehicle is being at a stop or is running based on outputs from the vehicle speed detection means and controls the driving of the actuators at certain intervals while the vehicle is being at a stop, whereas while the vehicle is running, only when the vehicle is running stably where a state continues for a given length of time in which the speed of the vehicle is equal to or more than a given value, while the acceleration of the vehicle is equal to or less than a given value, the control means controls the driving of the actuators based on pitch angle data taken during the stable running of the vehicle, the headlamp leveling device is adapted to control the driving of the actuators only in a case where respective mean pitch angle data of a plurality of different cycle periods come to coincide with one another after the state continues for a given length of time in which the speed of the vehicle is equal to or more than a given value, while the acceleration of the vehicle is equal to or less than a given value.
In addition, according to a second implementation of the invention, a headlamp leveling device comprises headlamps adapted to be driven by actuators such that light axes thereof are tilted up and/or down relative to the body of a vehicle, control means for controlling the driving of said actuators, vehicle speed detection means for detecting the speed of the vehicle, pitch angle detection means provided on either of left and right suspensions of either of front and rear wheels for detecting the pitch angle of the vehicle, and a storage part for storing pitch angle data of the vehicle detected by the pitch angle detection means, the control means being adapted to control the driving of the actuators based on pitch angle data detected by the pitch angle detection means such that the light axes of the headlamps always stay in a predetermined tilted state relative to the surface of a road, wherein said control means determines whether the vehicle is being at a stop or is running based on outputs from said vehicle speed detection means and controls the driving of the actuators at certain intervals while the vehicle is being at a stop, whereas while the vehicle is running, only when the vehicle is running stably where a state continues for a given length of time in which the speed of the vehicle is equal to or more than a given value, while the acceleration of the vehicle is equal to or less than a given value, the control means controls the driving of the actuators based on pitch angle data taken during the stable running of the vehicle, the headlamp leveling device is adapted to control the driving of the actuators only in a case where the speed of the vehicle is equal to or more than a given value and the acceleration thereof is equal to or less than a given value and where a state continues for a given length of time in which respective mean pitch angle data of a plurality of different cycle periods coincide with one another.
In the headlamp according to the implementations, a reflector in which a light source is securely inserted may be constructed to tilt around a horizontal tilting shaft relative to a lamp body, and the light axis of the reflector (the headlamp) may be arranged to be tilted around the horizontal tilting shaft by the actuator.
The above implementations of the invention are premised on that the leveling (the correction of the light axes) is carried out based on the pitch angle data of the vehicle at a stop. The pitch angle is based on a tilt of the vehicle in the longitudinal direction. The pitch angle data of the vehicle when it is at a stop is more accurate than that of the vehicle when it is running by an extent that the former is less affected by disturbance factors than the latter. Since the driving of the actuators is controlled based on the more accurate pitch angle data, the actuators so controlled can in turn render a more accurate leveling of the headlamp.
Additionally, since the control of the driving of the actuators while the vehicle is at a stop is limited to given time intervals, the frequency at which the actuators are activated is reduced to that extent, and therefore, less power is needed. Also, the wear of the driving mechanism components can be reduced.
The leveling of the headlamps (the correction of the light axes) is based on a set of pitch angle data taken during a stable running condition, which is a state in which for a given length of time the speed of the vehicle is equal to or more than a given value and the acceleration is equal to or less than a given value, (which may be data close to the pitch angle data taken while the vehicle is at a stop). The data of the stable running condition can be used to correct the inappropriate leveling of the headlamps (the correction of the light axes) based on pitch angle data taken when the vehicle is, for example, parked along a slope or riding on a curb.
Furthermore, even if a stable running condition is met, pitch angle data obtained when the vehicle is turning, slaloming or running on badly irregular road surfaces may be inappropriate for leveling purposes. To address this issue, a set of respective mean pitch angle data for a different cycle period Is compared with one another. Whether those mean pitch angle data are appropriate is determined by comparing whether the respective mean pitch angle data coincide with one another. Only when they are determined as appropriate (coincide with one another), the driving of the actuators is controlled. This avoids inappropriate automatic headlamps leveling.
When the vehicle is turning, slaloming or running on irregular road surfaces, the effect of the turning G or the irregularities of the surface of the road are reflected on pitch angle data. The detected pitch angle data is clearly different from pitch angle data collected when the vehicle is running with no turning G acting on the vehicle or running on a road surface free from irregularities.
FIG. 3 is a diagram showing pitch angles detected on the vehicle that is slaloming. In the figure, a character A0 denotes the original waveform of pitch angle data detected, a character Al denotes the waveform of one-second mean pitch angle data, a character A2 denotes the waveform of two-second mean pitch angle data, and a character A3 denotes the waveform of three-second mean pitch angle data. When considering the respective mean pitch angle data of a plurality of cycle periods (1 second, 2 seconds, 3 seconds) in FIG. 3, as the cycle period becomes longer (1 second  less than 2 seconds  less than 3 seconds), the effect of change in signal from the vehicle height sensor appears later.
Consequently, unless there are factors affecting the pitch angle data, mean pitch angle data of different cycle periods will be identical to one another (i.e. it substantially coincides with one another), whereas if there are factors affecting the pitch angle data (for example, turning, slaloming or running on irregular road surfaces), mean pitch angle data of different cycle periods will be different from one another (it does not coincide with one another).
Whether the respective mean pitch angle data of the different cycle periods are appropriate is determined by deciding whether the respective mean pitch angle data coincide with one another. If they are appropriate, the driving of the actuator is arranged to be controlled, whereas if they are not, then the driving of the actuator is arranged not to be controlled.
According to the first implementation of the invention, respective mean pitch angle data of two different cycle periods, for example, one-second mean pitch angle data and three-second mean pitch angle data, are compared with one another. However, even if they are different pitch angle data as a result of the action of a certain disturbance factor on the vehicle, it is possible that both data may coincide at some points (e.g. positions P1, P2, P3, P4 in FIG. 3). According to the second implementation of the invention, not only are the respective mean pitch angle data, for example, one-second mean pitch angle data and three-second mean pitch angle data, compared with one another but also the appropriateness of those data is determined based on a coincidence of the two data over a given length of time. Therefore, a risk of the headlamp being leveled based on pitch angle data detected while a certain disturbance factor is acting on the vehicle is eliminated.
According to a third implementation of the invention, the mean pitch angle data of at least three durations of cycle periods are arranged to be compared with one another. Therefore, chances of leveling the headlamps based on pitch angle data detected while a certain disturbance factor is acting on the vehicle are reduced substantially or eliminated. Also, the time required to level the headlamps is short.
According to the first implementation of the invention, respective mean pitch angle data of two different cycle periods, for example, one-second mean pitch angle data and three-second mean pitch angle data, are compared with one another. Since the two mean pitch angle data colleted under a disturbance factor impinging on the vehicle may happen to coincide with one another, there may be a risk that the headlamp is leveled based on the inappropriate pitch angle data.
According to the second implementation of the invention, since the leveling of the headlamp is not carried out until the respective mean pitch angle data are compared with one another and also until a given length of time elapses. Thus, a certain time may be required before the headlamp is leveled.
According to the third implementation of the invention, the appropriateness of the respective mean pitch angle data is determined by deciding whether the respective mean pitch angle data of at least three different durations of cycle periods coincide with one another. Thus, the headlamp can be prevented from being leveled based on pitch angle data taken while the vehicle is under the influence of a disturbance factor. Furthermore, the time required to level the headlamp is short.